With the continuing demand for automobiles as means of transportation, there have arisen several social problems. Among them are air pollution and the consumption of fossil fuels, especially petroleum.
Some measures have been taken to reduce the amount of harmful substances in exhaust gas, but this has also caused a degradation of the overall efficiency of the internal combustion engine (hereafter referred simply to as engine). For the purpose of preventing a degradation of the operating efficiency of the engine and improving measures against exhaust gases, an electronic control apparatus has been employed which has an improved precision in control. For example, there have been proposed an electronically controlled fuel injection apparatus and an electronically controlled ignition timing apparatus, and most recently an ignition apparatus controlled by a microprocessor.
The conventional trend in such a control apparatus is toward the mere replacement of mechanical control by an electric one and therefore the individual controlled objects must be provided with the associated electronic control units.
The control of an engine should suppress the harmful components in exhaust gases and operate the engine with a high efficiency. The assembly of the separate electronic control units provided for the controlled objects, e.g. the electronically controlled fuel injection apparatus and the electronically controlled ignition timing apparatus, as described above, provides a poor interrelation among the control units so that a close control of the overall control system is impossible. Moreover, such a composite control system must be accompanied by very complicated circuits. For example, a circuit for detecting the irregular output of a sensor such as an angular position sensor is required.